This section provides background information related to the present disclosure which is not necessarily prior art.
Conventional heat exchangers having heat-exchanging tubes and fins comprising aluminum or an aluminum alloy are mostly designed so that the surface areas of heat-radiating portions and cooling portions are as large as possible, to obtain excellent heat-radiation or cooling effects in a limited space. Therefore, the gaps between the fins are very small. Also, to decrease air resistance of the heat exchanger to as low as possible, the fins are notched. The notched fin is referred to as a fin louver.
When the above-mentioned heat exchangers are used for cooling, the moisture contained in air is condensed on the surface of the heat exchanger to form water droplets which fill the gaps between the fins to increase the air resistance of the heat exchanger, and thus the heat-exchanging efficiency of the heat-exchanger is decreased. Also, the condensed water drops cause corrosion of aluminum or aluminum alloy in the heat exchanger, and thus a fine white powder of aluminum oxide is generated on the fin surfaces. To prevent the blockage of the heat exchanger by the water drops remaining in the gaps between the fins, treatment methods for imparting a high hydrophilicity to the fin surfaces and for enhancing the water-wetting property of the fin surfaces have been developed.
As a surface treatment for a purpose of preventing a corrosion of the aluminum or aluminum alloy heat exchanger, a chromic acid-chromate chemical conversion treatment, a phosphoric acid-chromate chemical conversion treatment, and non-chromate chemical conversion treatments are known. The chromic acid-chromate chemical conversion treatment was practically utilized from about 1950 and is still widely used for the fin materials of heat exchangers, etc. This chemical conversion treatment liquid contains, as main components, chromic acid (CrO3) and hydrofluoric acid (HF), and further an accelerator, and can form a chemical conversion coating containing a small amount of hexavalent chromium. The phosphoric acid-chromate chemical conversion treatment is based on the invention of U.S. Pat. No. 2,438,877 and the treatment liquid thereof comprises chromic acid (CrO3), phosphoric acid (H3PO4) and hydrofluoric acid (HF). The resultant chemical conversion coating contains, as a principal component, hydrated chromium phosphate (CrPO4.4H2O).
This process is, however, disadvantageous in that the coating procedure causes a waste liquid containing hexavalent chromium (Cr6+) to be discharged. Since the chromate type surface treatments use an aqueous treatment liquid containing harmful hexavalent chromium, there is a strong demand for a new treatment liquid containing no hexavalent chromium, to prevent environmental pollution. Also, since the above-mentioned waste liquid is not allowed to be discharged without a hexavalent chromium-removing treatment, the waste liquid must be treated by a treatment apparatus using treatment reagents which causes the resultant product to be expensive.
Vehicles often accumulate odors inside their cabins during their lifetime of use. Such odors can be caused in a variety of ways and by a variety of sources. For example, objects left inside the vehicle, volatile organic compounds (VOCs) from the cabin interior materials, activities such as smoking and eating and the accumulation of dust and other pollutants suspended in the air can all contribute to the accumulation of odors. Eventually odors inside a vehicle become annoying and in some cases they may become a health risk if the source of odor involves bacteria, mold (fungi) or other microorganisms.
One location for the growth and/or accumulation of hidden pollutants is in the interior of the air conditioning system. Typical air conditioning units include a chamber, where the refrigerant serpentine, also known as evaporator core, is embedded. Under normal operating conditions of a properly functioning air conditioning system, the serpentine condenses the moisture coming into the chamber due to the interaction between temperature, the existing dew point, and the relative humidity inside and outside the vehicle. In this process, the air entering the system contacts the cold interior parts of the system which retain and condense the humidity from the air. The cooler drier air comforts passengers once it exits the system, vents, and enters the vehicle cabin.
Cigarette smoke generated in the interior of an automobile will be channeled eventually through the automobile's heat exchanger system. Often, the odor remains resilient to removal, depreciates the value of the automobile and causes irritation to passengers.
In addition, some of the pollutants pass through the system and can become deposited over the interior surfaces of the cabin. The accumulated particles on the moist surfaces of the evaporator provide an environment in which micro-organisms can grow, particularly in the absence of UV light from the sun. The growth of microbial pollutants inside the evaporator further increases the amount of pollutants and odors that can enter the cabin in the airflow created by the blower.
The mold can generate spores that can become suspended in the air inside the cabin. These spores can then re-circulate through the air conditioning system. Because of the moisture and temperature activity inside the evaporator and the lack of light, many of these contaminants and particles tend to accumulate inside the evaporator unit, creating layers of what appears to be “mud”. When the air conditioning is turned on spores in the system can be blown out into the cabin which can actually create a health risk in certain individuals. At best, this situation creates an annoying bad-smelling odor every time the A/C and/or the heater are turned on.
Methods for removing or treating these mold, bacteria and odors inside the evaporator and ventilation system have been developed. One method is to spray a foaming aerosol solution through the evaporator drain hole. The foam then expands into foam inside the evaporator. However, the rapid expansion from an aerosol to a foam state prevents the foam from effectively reaching the upper recesses of the evaporator. In addition, the method is complicated by the need to either remove the evaporator or raise the vehicle on a lift in order to reach the drain hole, or drill a hole in the evaporator case to allow a straw type aerosol injector access. These are all labor intensive operations requiring a person to position the vehicle appropriately, position and hold the aerosol can while depressing the valve releasing its contents.
Another method involves spraying a non-foaming aerosol solution into the exterior-located air intake, while the blower motor is running. However, because the aerosol droplets of the spray are heavier than air, and significantly larger at about 40-100 microns in size. They do not travel effectively and far enough to reach the inside of the evaporator or the entire ventilation system. Neither of these solutions is designed to treat interior cabin surfaces for microorganisms and contaminants and both are labor-intensive in that the operator must continuously depress the valve on the aerosol can in order to release its contents. Airsept, Inc. provides one such product. Alternatively, electronics can be used to keep the evaporator dry. See e.g., U.S. Pat. Nos. 5,899,082 and 6,840,051.
Accordingly, is desirable to provide a corrosion resistance coating for an automotive heat exchanger component comprising an odor remediation coating, and a process for making such a heat exchanger component that is at least as reliable for making heat exchanger component surfaces requiring a relatively high level of corrosion resistance as that provided by conventional chromate and non-chromate chemical conversion coating methods.